If you studied Spanish, the first thing you learned is that nouns have gender. “The moon” is la luna (feminine) and “the sun” is el sol (masculine). Some words change their ending to accomodate gender: “the boy” is el niño and “the girl” is la niña. There’s not always a lot of logic behind this – why is “speed” feminine, la rápidez, and “waste” mascuine, el derroche? – so you simply have to memorize the gender.
But wait! There’s (always) more to learn.
Some nouns are epicene. That means they have the same article (el or la) and the same word for both sexes. For example, “the goat” is la cabra. If you want to specify the sex, you say la cabra macho, “the male goat,” or la cabra hembra, “the female goat.” A number of animals are epicene, such as “the squirrel,” la ardilla, and “the vulture,” el buitre. There’s no logic, so rote memorization is your only recourse.
Some nouns are gender common. That means the word stays the same, but the article changes to show if the person being referred to is male or female. Quite a few words fall into this category. “The artist” is la artista or el artista, “the soldier” is la soldado or el soldado, and “the martyr” is la mártir or el mártir. When you memorize the word, you have to memorize how to use it.
A smaller list of words are gender ambiguous. “The sea” can be masculine or feminine, la mar or el mar, as can “the sugar,” la azúcar or el azúcar. If you have any free brain cells left, memorize these details, too.
(Some words change their meaning completely depending on whether they are feminine or masculine. El cometa is “the comet” and la cometa is “the kite.” Memorize these if your brain hasn’t exploded yet.)
Finally, Spanish has no neutral nouns, but it has some neutral pronouns: esto, eso, aquello, ello, lo. But now we’re getting into grammar, and I’m not going there today. Mercifully.
— Sue Burke